Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$57.40	11.634%	$64.0779	$64.08	$64.10	$64.10
Purchase #2	$94.68	13.367%	$107.3359	$107.34	$107.35	$107.30
Purchase #3	$240.53	5.555%	$253.8914	$253.89	$253.90	$253.90
Purchase #4	$160.53	11.284%	$178.6442	$178.64	$178.65	$178.60
Purchase #5	$52.43	13.109%	$59.303	$59.30	$59.30	$59.30
Purchase #6	$102.54	8.148%	$110.895	$110.90	$110.90	$110.90
Purchase #7	$59.56	12.669%	$67.1057	$67.11	$67.10	$67.10
7 purchase totals =	$767.67		$841.2531	$841.26	$841.30	$841.20